1. Field of the Invention
The present invention relates to a wireless IC device, and in particular, relates to a wireless IC device used for an RFID (Radio Frequency Identification) system and a coupling method for a power feeding circuit and a radiation plate included in the wireless IC device.
2. Description of the Related Art
In the past, as a management system for goods, there has been developed an RFID system in which communication between a reader/writer generating an induction electromagnetic field and a wireless tag (also referred to as a wireless IC device) storing therein predetermined information assigned to goods is established on the basis of a non-contact method and information is transmitted. As a wireless tag used for this type of RFID system, in Japanese Unexamined Patent Application Publication No. 10-293828, a data carrier is described that includes an IC circuit, a primary coil antenna, and a secondary coil antenna and causes the primary coil antenna and the secondary coil antenna to be electromagnetically coupled to each other.
However, in the above-mentioned data carrier, the degree of coupling between the primary coil antenna and the secondary coil antenna is small, and a coupling loss occurs. While it is possible to improve the degree of coupling of a magnetic field by increasing the inductance value of the secondary coil antenna, this results in the secondary coil antenna being large in size. In addition, since the coupling depends on a communication frequency, it is difficult to decrease the size of the secondary coil antenna. Furthermore, when both the antennas are also electric-field-coupled to each other, there occurs a problem that the degree of coupling is small, in the same way as described above.